DEGENERATION IN BREEDING INSTINCTS. ne 
produced by the Helix are different from those produced by the Acha- 
tinella. The short-legged lamb, from which sprang the Ancon sheep, 
was not the suckling of a lioness, but had a sheep for its dam. In 
other words, the segregations and survivals of one generation control 
the types of heredity and variation (including mutation) in the next 
generation. 
Second Lesson.—If the selection of individual variations is necessary 
for the maintenance of the normal standard of eyesight in the human 
species, is it not possible that the same necessity exists in other 
species? And may it not be true that many other inherited endow- 
ments are subject to gradual decay when the standard of selection is 
lowered? If we find, in a given country, that the mothers who have 
to feed their babes on artificial substitutes for mother’s milk lose a 
larger per cent of their children than do those who are able to give 
suck, does it necessarily follow that the power of giving suck is in- 
creasing from generation to generation among the people of that 
country? In the language of the statistical method, is it not possible 
that the ‘‘skewness”’ of the ‘‘frequency curve”’ (for different grades 
in the power of furnishing milk) might, in such a case, give some 
indication of the selection that is taking place, and that, at the same 
time, the statistics of successive generations might show that there 
was no gain in the power? Or, in such a case, would there be no 
skewness in the frequency curve, though there is constant selection 
that results in the maintenance of a constant standard? 
20. Degeneration in Breeding Instincts. 
In the case of the Old World cuckoo it may be a question whether 
the loss of the maternal instinct (or rather of this series of instincts), 
came in a single generation, by one mutation, maintaining its type 
with constancy from the first; or by several successive mutations, 
each mutation being added to the previous ones, and being persist- 
ently inherited; or whether the process has been a very gradual ac- 
cumulation of individual tendencies through the success of aberrant 
individuals in leaving descent, and so lowering the general standard 
of service for the whole species. There are, however, certain facts 
that point toward the last of these as the process by which the degen- 
eration has taken place. F. M. Chapman, in his Handbook of Birds 
of Eastern North America, notes that ‘‘Many species [of cuckoo] are 
remarkable for the irregularity of their breeding habits.’”’ Of the 
Ani, a genus of the same family, he says: ‘‘The Anis are communistic, 
and build but one nest, in which several females lay and share the 
task of incubation.’”’ Now, it is manifest that, ina community of this 
